Outboard propulsion unit exhaust discharge system

ABSTRACT

It is disclosed for an engine driven outboard propulsion unit having a reversible propeller to selectively drive the propulsion unit in forward and reverse directions and passage means for conducting the exhaust gases from the engine through said unit, a pair of underwater discharge openings for said propulsion unit and respectively disposed fore and aft of the propeller to provide for selective exhaust discharge into the outflow of the propeller slipstream regardless of the direction of propulsion unit operation and thereby assure a solid flow of water to the propeller in both forward and reverse directions of operation of the propulsion unit.

[ Mar. 18, 1975 1 OUTBOARD PROPULSION UNIT EXHAUST DISCHARGE SYSTEM [75]Inventor: Richard II. Snyder, Oshkosh, Wis.

[73] Assignee: Brunswick Corporation, Chicago,

Ill.

22 Filed: Jan. 31, 1969 21 Appl.No.:795,434

Shimanckas 416/93 Primary ExaminerTrygve M. Blix AssistantExaminerStuart M. Goldstein Attorney, Agent, or FirmRoy Montgomery [57]ABSTRACT It is disclosed for an engine driven outboard propulsion unithaving a reversible propeller to selectively drive the propulsion unitin forward and reverse directions and passage means for conducting theexhaust gases from the engine through said unit, a pair of underwaterdischarge openings for said propulsion unit and respectively disposedfore and aft of the propeller to provide for selective exhaust dischargeinto the outflow of the propeller slipstream regardless of the directionof propulsion unit operation and thereby assure a solid flow of water tothe propeller in both forward and reverse directions of operation of thepropulsion unit.

27 Claims, 16 Drawing Figures PATENTEUHAR 1 81975 R SHEET l I]? 5INVENTOR. RICHARD H SNYDER BY 7 f A,f2@)Z24 Attorneys FIG -2 PATENTEU3,871,324

sum 3 BF 5 INVENTOR RICHARD H SNYDER PMEIJTEU 1 8 i975 3. 87 l 324 SHEETu of 5 INVENTOR! RICHARD H. SNYDER BY 7 w 54%, av /M Attorneys wgmgum 181975 3.8

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REVERSE TH RUST (LBS) A FOR A THROUGH THE HUB EXHAUST PROPELLER ENGlNETWO BLADES, 2| PITCH SPEED (RPM) B O D REAR EXHAUST OPEN REAR EXHAUSTOPEN REAR EXHAUST CLOSED NO FORWARD EXHAUST FORWARD EXHAUST OPEN FORWARDEXHAUST OPEN I500 A 20 so I I50 2000 as v 225 255 INVENTOR. FIG 16RICHARD H. SNYDER Jinx/f Attorneys OUTBOARD PROPULSION UNIT EXHAUSTDISCHARGE SYSTEM This invention relates to an exhaust discharge systemfor outboard propulsion units.

In the case of inboard-outboard drives for watercraft and outboardmotors it has been common practice to conduct the engine exhaust gasesthrough the drive shaft housing of the drive unit or motor for dischargeunderwater. The discharge is generally rearwardly of the propellereither through the propeller hub or through an exhaust snout associatedwith or projecting beneath the anti-cavitation plate of the propulsionunit. When the propulsion unit is operating in the forward direction,such discharge is into the outflow side of the propeller slipstream andgenerally does not affect the solid" flow of water to the propeller.When the propulsion unit is operated in reverse, however, the propellerblades cavitate' in the froth created by the discharge of the exhaustgases into the inflow side of the propeller slipstream to greatly impairthe reverse propeller thrust. Also when operating in reverse, theexhaust passage is substantially blocked by water giving rise to a backpressure on the engine exhaust ports to adversely affect the efficiencyof the engine and further impair the reverse propeller thrust. It isgenerally an object of this invention to provide for discharge ofexhaust gases into the outflow side of the propeller slipstream duringreverse operation as well as in forward operation and thereby assuresolid flow of water'to the propeller in both forward and reversedirections of operation of the propulsion unit. A further object is tosubstantially reduce the back pressures in the exhaust system generallyattendant with reverse operation of the propulsion unit.

Generally, the invention relates to an outboard propulsion unit drivenby an internal combustion engine and having a reversible propeller toselectively drive the unit in forward and reverse directions and furtherhaving passage means for conducting the exhaust gases from the engine.According to the invention, the propulsion unit includes means definingan underwater exhaust discharge opening generally rearwardly of thepropeller and communicating with the exhaust passage means to providefor discharge of the engine exhaust gases rearwardly of the propellerwhen the propeller is operating to drive the propulsion unit in theforward direction. The propulsion unit further includes means defining asecond underwater exhaust discharge opening generally forwardly of thepropeller and which is normally closed when the unit is operated in theforward direction. The second exhaust discharge opening is adapted toopen and provide for discharge of the exhaust gases forwardly of thepropeller when the propeller is operating to drive the propulsion unitin the rearward or reverse direction. The invention thus provides forsolid flow of water to the propeller in both forward and reversedirections of operation of the propulsion unit.

The drawings furnished herewith illustrate the best mode of carrying outthe invention as presently contemplated and described hereinafter.

In the drawings:

FIG. 1 is a side elevation of an outboard motor which embodies theinvention;

FIG. 2 is an enlarged partial sectional view of the propeller and itsmounting for the motor of FIG. 1 and shows a construction wherein thepropeller is separable from the slip clutch mounting and wherein thepropeller is positioned in the forwarddrive position;

FIG. 3 is a partial sectional view taken generally on 33 of FIG. 2;

FIG. 4 is a view generally similar to that of FIG. 2 and shows thepropeller in the reverse drive position;

FIG. 5 is an enlarged partial sectional view of a propeller and itsmounting wherein the propeller is separable from the slip clutchmounting but movable there with and shown in the forward drive position;

FIG. 6 is a view generally similar to that of FIG. 5 and shows theseparable propeller and slip clutch in the reverse drive position;

FIG. 7 is an enlarged partial side elevational view of a propeller andits mounting wherein the propeller is not normally separable from itsslip clutch mounting and shows the propeller in the forward driveposition;

FIG. 8 is a view generally similar to that of FIG. 7 and shows thepropeller in the reverse drive position;

FIG. 9 is a partial side elevational view of a propeller and itsmounting generally similar to that of FIG. 7 but shows a different formof closure plate at the exhaust discharge opening, showing in solidlines the position of the propeller for forward drive operation and inphantom lines the position of the propeller for reverse drive operation;

FIG. 10 is a partial side elevational view of a further embodiment ofthe propeller and its mounting according to this invention, showing insolid lines the position of the propeller for forward drive operationand in phantom lines the position of the propeller for reverse driveoperation;

FIG. 11 is a partial side elevational view of a still further embodiment-of the invention showing the propeller, its mounting and shaft, andshowing in solid lines the position of the propeller for forward driveoperation and in phantom lines the position of the propeller for reversedrive operation;

FIG. 12 is a view generally similar to that of FIG. 11 and shows anembodiment along with reversing gear means on the propeller shaft;

FIG. 13 is a partial side elevation of an outboard propulsion unitshowing a further embodiment of the invention wherein an exhaustdischargesnout is disposed rearwardly of the propeller;

FIG. 14 is a sectional view taken generally on line 14-14 of FIG. 13;

FIG. 15 is a detail view taken generally on line 1515 of FIG. 13; and

FIG. 16 is a table setting forth data generally showing the improvementin reverse propeller thrust which results from a utilization of thisinvention.

Referring to the drawings, an outboard propulsion unit for watercraftsuch as the outboard motor 1 includes an internal combustion engine 2within the cowl enclosure 3 at the upper end of the motor for driving apropeller 4 at the lower end thereof. Driving rotation of propeller 4 isselectively reversible by means, not shown, to provide for operation ofmotor I in forward and reverse directions as desired. The exhaust gasesfrom the engine 2 are conducted through passage means 5 in the lowerhousing portion 6 of the motor I for underwater discharge generallyrearwardly of the propeller 4 in a manner further described hereinafter.

According to the embodiment shown in FIGS. 2 through 4, the propeller 4is independently replaceable,

if desired or when need be, relative to the slip clutch assembly 7 onwhich it is carried. The assembly'7 comprises inner and outer sleevemembers 8 and 9 respectively, between which an elastomeric annulus 10 issandwiched. The inner sleeve 8 is rotationally locked relative to thegenerally horizontal propeller shaft 11 by engagement of complementaryaxial splines 12 and 13 on sleeve 8 and shaft 11, respectively, and isaxially secured on the shaft between the forwardly disposed annular stopcollar 14 engaged with the tapered shoulder 15 on the shaft and theannular retainer member 16 disposed rearwardly on the shaft.

The propeller 4 includes an outer hub member 17 which carries the blades18 and an inner hub member 19 spaced radially inwardly from andconnected to the outer hub member 17 by a plurality of circumferentiallyspaced vanes 20. The several vanes 20 divide the annular space betweenthe hub members 17 and 19 into a plurality of axially extending passages21 which communicate with the passage means 5 through the opening 22rearwardly of the lower housing portion 6 and serve to conduct theengine exhaust gases rearwardly for discharge underwater through therearwardly disposed propeller hub opening 23.

The separable propeller 4 is rotationally locked onto the outer sleeve 9of the slip clutch assembly 7 by engagement of complementary axiallyextending splines 24 and 25 on the sleeve and propeller, respectively.Propeller'4 is movable axially to the slip clutch assembly 7 andshaft'll, and is biased forwardly into engagement with the stop collar14 by the coil spring 26 disposed between the retainer member 16 and theannular shoulder seat 27 formed by the rearwardly disposed internaloffset 28 on the inner propeller hub member 19. With the propeller 4 inengagement with the stop collar 14 as generally shown in FIG. 2, theouter hub 17 overlaps within the opening 22 of housing portion 6 toprovide a generally continuous passage for the exhaust gases from thepassage means 5 in housing portion 6 into the propeller hub passages 21.During forward drive operation, the propeller thrust as well as spring26 tend to maintain the propeller 4 forwardly and the exhaust gases passthrough the passages 21 for discharge into the outflow side of thepropeller slipstream through the discharge opening 23. The retainermember 16 on the end of the propeller shaft 11 is rotationally locked onthe shaft by engagement of the complementary splines 29 and 13 on theretainer member and shaft, respectively, and engages with the end of theinner sleeve 8 of the slip clutch assembly 7 to secure the assemblyagainst the stop collar 15. Member 16 carries a peripherally disposedannular resilient valve member 30 which in the forward position of thepropeller 4 is spaced from the outer hub member 17 to define the annularcharacter of discharge opening 23. The propeller 4, slip clutch assembly7 and retainer member 16 are secured on the propeller shaft 11 by thelock washer 31 and nut 32 disposed on the end of the shaft.

As explained, during forward drive operation of the outboard motor 1,propeller rotation develops a thrust which along with the biasing forceof spring 26 tends to maintain the propeller 4 forwardly against thestop collar 14 as generally shown in FIG. 2 to provide for discharge ofthe engine exhaust gases into the outflow side of the propellerslipstream through the discharge opening 23. When the propeller rotationis reversed for reverse drive operation of the motor 1, the thrustdeveloped by the propeller 4 is also reversed forcing the propeller tomove rearwardly relative to the slip clutch assembly 7 and shaft 11against the biasing pressure of spring 26 as generally shown in, FIG. 4.With rearward movement of the propeller 4 upon reverse drive operation,the inner hub member 19 of the propeller moves under thrust to engagethe retainer member 16 and the valve member 30 engages with the outerhub member 17 to close the discharge opening 23 against egress ofexhaust gases into what is now the inflow side of the propellerslipstream. The movement of the propeller rearwardly causes a separationbetween the propeller 4 and the housing portion 6 to form the radialopening 33 therebetween to provide for discharge of the engine exhaustgases. The gases passing through opening 33 during reverse driveoperation enter the outflow side of the propeller slipstream so that thepropeller 4 acts on a solid flow of water to the blades 18 instead ofcavitating in a froth created by the exhaust gases as was heretofore thepractice when the gases were discharged from the opening 23 regardlessof the direction of operation for the motor 1. As a result, the thrustdeveloped by the propeller during reverse drive operation issubstantially increased to provide for better and more positive controland maneuverability in reverse for the motor 1 and watercraft driventhereby.

When the outboard motor 1 is placed in neutral, the coil spring 26 willbias the non-rotating propeller 4 to its forward position and the springwill maintain the propeller forwardly when the engine 2 is shut off.Since the spring 26 biases the propeller 4 to its forward position whenthe engine 2 is shut off, any corrosion or marine growth would tend tofreeze" or seize the propeller in that position. and during subsequentoperation, the motor 1 would still be capable of normal forwardoperation without exhaust leakage ahead of the propeller. Until such afreeze condition is corrected, reverse operation of the motor I will beinefficient while the exhaust flows through the propeller 4 into theinflow side of the propeller slipstream.

The embodiment of FIGS. 5 and 6 show a separable propeller 34 and slipclutch assembly 35 which though separable move together as a unitrelative to the propeller shaft 36 in response to propeller thrust toprovide for engine exhaust discharge into the outflow of the propellerslipstream for both forward and reverse drive operation.

Referring to FIG. 5, the slip clutch assembly 35 generally includesinner and outer hub sleeve members 37 and 38, respectively, having anelastomeric annulus 39 sandwiched therebetween. The assembly 35 isrotationally locked on the shaft 36 by engagement of the complementarysplines 40 and 41 on the inner hub member and shaft respectively. Theseparable propeller 34 having radially spaced inner and outer hub sleevemembers 42 and 43, respectively, is rotationally locked on the slipclutch assembly 35 by engagement of the complementary splines 44 and 45between the propeller inner hub member 42 and the slip clutch outer hubmember 38. The slip clutch outer hub member 38 and the propeller innerhub member 42 are generally confined axially between the enlargedstepped forward portion 46 on the inner hub member 37 and the radialflange 47 on nut 48 threaded onto the rearward end of the member 37 toform a unitary assembly, with adequate clearance being provided for thehub member 38 to permit the slip clutch to yield in response tovibration and/or shock loading. Some axial clearance may also beprovided for propeller hub member 42 to permit slight axial movement ofthe propeller relative to the slip clutch sleeve member 38 with changesin thrust to prevent corrosion buildup therebetween.

The radially spaced hub sleeve members 42 and 43 of propeller 34 areconnected by a plurality of circumferentially spaced vanes 49 formingaxially extending passages 50 for conducting engine exhaust gasesthrough the propeller for discharge through the opening 51 rearwardlythereof. The blades 52 are carried on the outer hub member 43 of thepropeller.

The unitary assembly comprising the propeller 34 and slip clutchassembly 35 is movable axially on shaft 36 and is shown biased forwardlyby the coil spring 53 in FIG. 5 to place the inner hub member 37 of theslip clutch assembly into engagement with the annular tapered shoulder54 on the shaft. In the forward position of the unitary assembly theouter sleeve member 43 of propeller 34 is overlapped within the opening22 of the lower housing portion 6 to place the propeller hub passages 50in communication with the passage means 5 of the lower housing portion.

The coil spring 53 is disposed between the flanged nut 48 ofthe unitaryassembly and the retainer member 55 which has a forwardly facing annularrecess 56 for seat-ing the rear end of the spring. The retainer member55 is rotationally locked on the shaft 36 by engagement of thecomplementary splines 57 and 41, respectively,

and carries the annular valve member 58 peripherally thereof. The lockwasher 59 and nut 60 confine the retainer member 55 aftward.

In forward drive operation, the unitary assembly including propeller 34tends to remain forwardly against the tapered shoulder 54 on the shaft36 under the influ ence of propeller thrust and the spring 53 asgenerally shown in FIG. 5 so that the exhaust flow from the passagemeans 5 in lower housing portion 6 is conducted rearwardly through thepropeller passages 50 for discharge from the opening 51 into the outflowof the propeller slipstream. When propeller rotation is reversed forreverse drive operation, the reversal in propeller thrust forces theunitary assembly rearwardly away from shoulder 54 against the pressureof spring 53 as generally shown in FIG. 6. The rearward movement of theunitary assembly upon reverse drive operation carries the outer hubmember 43 of the propeller 34 into circumferential engagement with thevalve member 58 to close the discharge opening 51 generally preventingthe egress of exhaust gases into what is now the inflow side of thepropeller slipstream. The movement of the unitary assembly rearwardlyduring reverse drive operation effects a separation between thepropeller 34 and the lower housing portion 6 to form the radial exhaustdischarge opening 61 therebetween for discharging the exhaust gases intothe outflow of the propeller slipstream leaving the propeller 34 to acton a solid flow of water to the blades 52.

In the embodiment of FIGS. 7 and 8 the propeller 62 and slip clutch areconsidered to be non-separable and together move relative to thepropeller shaft 63 in response to propeller thrust to provide for engineexhaust discharge into the outflow of the propeller slipstream for bothforward and reverse drive operation.

Referring to FIG. 7, the propeller 62 is carried on the generallyhorizontal propeller shaft 63 and includes an inner hub sleeve member 64rotationally locked on the shaft by engagement of complementary splines65 and 66 on the hub member and shaft, respectively. An intermediate hubsleeve member 67 is spaced outwardly from hub member 64 and anelastomeric annulus 68 is sandwiched therebetween to form a slip clutch.The intermediate hub member 67 is generally confined axially at therespective ends thereof by the enlarged stepped portion 69 at theforward end of the inner hub member 64 and rearwardly by the radialflange 70 on the nut member 71 threadedly engaged externally on the hubsleeve 64, though adequate clearance is provided between the hub sleevemembers 64 and 67 to permit the slip clutch to yield in response tovibration and/or shock loading.

The propeller 62 also includes an outer hub sleeve member 72 which isspaced outwardly from the hub sleeve member 67 and carries-the blades73. A plurality of circumferentially spaced vanes 74 connect the outerand intermediate hub sleeve members 72 and 67 to form axially extendingpassages 75 through the propeller 62.

The propeller 62 is axially movable on shaft 63 and is biased forwardlyby the coil spring 76 placing the inner hub sleeve member 64 intoengagement with the annular tapered shoulder 77 on shaft 63 with theouter hub sleeve member 72 overlapping within the opening 22 of thelower housing portion 6. The coil spring 76 is disposed between theflanged nut member 71 and a forwardly facing annular recess 78 in valveretainer member 79 spaced rearwardlyfrom the nut member 71. The retainermember 79 carries a peripherally disposed annular resilient valve member80 which as shown in FIG. 5 is spaced from the outer hub member 72 atthe exhaust discharge opening 81. Retainer member 79 is rotationallylocked on shaft 63 by engagement of complementary splines 66 and 82 onthe shaft and retainer member, respectively, and is biased rearwardly bythe spring 76. Retainer member 79 has a hexagonal pocket 83 into whichthe nut 84 fits, thus locking the nut 84 against backing off. The spring76 biases the retaining member 79 into engagement with the nut 84, butthe retaining member can be manually moved forward, thus allowing thenut to be removed without the use of special tools.

' In forward drive operation as generally shown in FIG. 7, the propeller62 tends to remain forwardly against shoulder 77 under the influence ofpropeller thrust and the spring 76 so that the exhaust flow is conductedrearwardly through the propeller passages 75 for discharge from theopening 81 into the outflow of the propeller slipstream. When propellerrotation is reversed for reverse drive operation, the reversal inpropeller thrust forces the propeller 62 rearwardly away from the stopshoulder 77 against the pressure of spring 76 and moves the outer hubmember 72 into circumferential engagement with the valve member 80 toclose the discharge opening 81 against egress of exhaust gas into whatis now the inflow side of the propeller slipstream as generally shown inFIG. 8. The movement of propeller 62 rearwardly during reverse driveoperation effects a separation between the propeller and the lowerhousing portion 6 forming the radial exhaust discharge opening 85therebetween for discharging the exhaust gases into the outflow of thepropeller slipstream leaving the propeller to act on a solid flow ofwater to the blades 73.

The embodiment of FIG. 9 is generally similar to that of FIGS. 7 and 8but showing another form of valve member to close the exhaust dischargeopening 81. According to FIG, 9, a metal valve plate 86 is utilized inplace of the annular resilient member 80 of the previous figures and isformed integral with the retainer member 87. The retainer member 87 isrotationally locked on shaft 63 by engagement of the complementarysplines 66 and 88 on the shaft and retainer member, respectively, and anannular forwardly facing recess 89 is provided in the retainer memberfor seating the corresponding end of the coil spring 76.

Operation for the embodiment of FIG. 9 is generally similar to theembodiment of FIGS. 7 and 8 in that the propeller 62 is thrust sensitiveand moves relative to shaft 63 to provide for engine exhaust dischargeinto the outflow of the propeller slipstream for both forward andreverse drive operation. However, rearward travel of the propeller 62 ishalted by engagement between the outer hub member 72 and the generallyrigid metal plate valve member 86 as'generally indicated by phantomlines in FIG. 9.

In the embodiments heretofore described, the propellers were thrustsensitive to provide for exhaust discharge into the outflow of thepropeller slipstream in both forward and reverse drive operation.According to FIG. the propeller 90 is torque sensitive with the shaft 91and inner hub member 92 having complementary helical splines or screwthreads 93 and 94, respectively. During forward drive operation, therotation of shaft 91 along with the biasing pressure of spring 95 tendsto force the propeller 90 in the direction of the tapered shoulder orstop 96 on the shaft. With the propeller 90 disposed forwardly, theengine exhaust gases are conducted rearwardly through the propellerpassages 97 formed by the circumferentially spaced vanes 98 connectingthe intermediate and outer hub sleeve members 99 and 100 for dischargerearwardly through the discharge opening 101 into the outflow of thepropeller slipstream. A reversal in the rotation of shaft 91 for reversedrive operation forces the propeller 90 rearwardly against the pressureof spring 95 and in the direction of the retainer member 102 which isrotationally locked on the shaft by engagement of complementary splines103 and 104 and carries the annular resilient valve member 105. Withrearward movement of the propeller 90 as shown in phantom lines in FIG.10, the discharge opening 101 is closed as the valve member 105 engageswith the outer hub member 100 and the resultant separation between thepropeller and housing portion 6 forms the radial opening 106 fordischarge of the engine exhaust gases into the outflow of the reversedrive propeller slipstream.

Referring now to the embodiment of FIG. 11, the propeller 107 is carriedon the generally horizontal propeller shaft 108 rotatably supportedwithin the bore 109 of the housing portion 110. The propeller 107 isfixedly secured on its shaft 108 and together they are selectivelyrotatable in opposed directions in accordance with forward and reversedrive operation by the generally vertical drive shaft 111 through themeshing bevel gears 112 and 113, with the gear 113 being rotatablylocked onto the propeller shaft by engagement of the complementarysplines 114 and 115, respectively. The drive shaft 111 is driven from anengine, not shown, whose exhaust gases are conducted downwardly throughthe passage means 116 in the housing portion and into the bore 109around the spoollike bearing retainer 117 for discharge underwater ashereinafter described.

The propeller 107 and its shaft 108 are movable axially relative to thebore 109 in response to propeller thrust with such movements beingcontrolled by the spring retainer 118 fixedly secured on the shaftbetween the bevel gear 113 and the forwardly disposed tapered rollerbearing 119. An expandable bellows type seal 120 is disposed between theshaft 108 and the rear end of the spool-like bearing retainer 117 toprotect the bearings and gears against ingress of water.

During forward drive operation of the propeller 107, the propellerthrust as well as the biasing pressure of spring 121 disposed betweenthe gear 113 and spring retainer 118 tend to maintain the propeller andits shaft 108 forwardly. In the forwardmost position of the propeller107 and its shaft 108, the spring retainer 118 engages the inner race ofthe tapered roller bearing 119 as a stop while the propeller overlapswithin the rearwardly facing opening 122 of the housing portion 110 asgenerally shown in solid lines in FIG. 11. The exhaust gases duringforward drive operation, flow from the housing portion passage means 116into the bore 109 and thence through the opening 122 into the passages123 of the propeller 107 formed by the circumferentially spaced vanes124 connecting the spaced hub sleeve members 125 and 126 for dischargerearwardly through the propeller discharge opening 127 into the outflowof the propeller slipstream.

During reverse drive operation of propeller 107, the reversal in thrustforces the propeller and its shaft 108 rearwardly against the pressureof spring 121 causing a separation between the propeller and housingportion 110 to form the radial exhaust discharge opening 128therebetween as generally shown by the phantom lines in FIG. 11. In therearmost position of the propeller 107 and its shaft 108, the springretainer 118 engages the bevel gear 113 as a stop and the spring 129disposed between the spring retainer and the inner race of the taperedroller bearing 119, though weaker than the spring 121, serves to holdthe inner race of the roller bearing in place. While the propellerexhaust discharge opening 127 is not closed by a valve, and water isallowed to enter the passages 123 during reverse drive operation, yetreverse propeller thrust is considerably improved as a substantial partof the exhaust gases take the route of least resistance and aredischarged through the opening 128 into the outflow of the propellerslipstream. I

The embodiment of FIG. 12 is in some respects similar to FIG. 11 andshows reversing gear means 130 in combination with the axially movablepropeller shaft 131 on which the propeller 132 is fixedly secured. Thereversing gear means 130 comprise axially aligned, opposed forward andreverse bevel gears 133 and 134, respectively, disposed in the bore 135of the housing portion 136 in meshing engagement with and on oppositesides of the bevel gear 137 secured on the lower end of the generallyvertical drive shaft 138. The bevel gears 133 and 134 are freelyrotatable on the propeller shaft 131 and are driven in opposeddirections by the drive gear 137. The driven gears 133 and 134 areselectively clutched to the propeller shaft 131 to drive the shaftcorrespondingly by the clutch element 139 fixedly secured onto the shaftbetween the driven gears. A cam actuator 140 is carried at the lower endof the rotatable shift rod 141 and is engageable with the forward end ofthe propeller shaft 131 to provide for selective movement of the shaftand clutch element 139 within the bore 135 into forward drive, neutral,and reverse drive positions. The drive shaft 138 is driven from anengine, not shown, whose exhaust products are conducted downwardlythrough the drive shaft housing passage 142 and into the bore 135 aroundthe spool-like bearing retainer 143 for discharge rearwardly through theopening 144 at the rear of the housing portion 136.

When forward drive operation is contemplated for the embodiment of FIG.12, the cam actuator is moved to a corresponding position to permit thecoil spring 145 disposed between the clutch element 139 and the reversegear 134 to bias the clutch element into engagement with the forwardgear 133. In the forward drive position, the propeller 132 is somewhatoverlapped within housing opening 144 and the engine exhaust gases movethrough the opening into the propeller passages 146 formed between thecircumferentially spaced vanes 147 connecting the-radially spacedpropeller sleeve members 148 and 149 for discharge rearwardly throughthe rear propeller opening 150 into. the outflow of the propellerslipstream.

When reverse drive operation is contemplated, the propeller shaft 131together with the propeller 132 are moved axially rearwardly to theposition shown in phantom lines in FIG. 12 against the pressure of coilspring 145 by the cam actuator 140 to engage the clutch element 139 withthe reverse gear 134. Simultaneously the radial exhaust opening 151 isformed where the propeller 132 and housing portion 136 separate. As wasthe case in the embodiment of FIG. 11, the discharge opening 150 at therear of the propeller 132 is not closed by a valve, but neverthelesspropeller thrust is considerably improved as a substantial part of theexhaust gases are discharged through the radial opening 151 into theoutflow of the propeller slipstream.

The embodiment of FIGS. 13-15 shows the invention as applied to anoutboard propulsion unit 152 having a lower housing portion 153 fromwhich the engine exhaust gases are discharged underwater at a locationadjacent to the anti-cavitation plate 154 and generally rearwardly fromthe propeller 155 as by an exhaust snout 156 projecting beneath theanti-cavitation plate. The propulsion unit 152 includes reversing gearmeans 157 whereby the propeller 155 may be selectively driven in opposeddirections corresponding to forward and reverse drive operation. Thereversing means 157 are controlled by a cam actuator 158 selectivelymovable by the rotatable shift rod 159. The vertically disposed driveshaft 160 is driven from an engine, not shown, the exhaust products ofwhich are conducted downwardly through the lower housing passage 161.The passage 161 divides into two branch passages 162 and 163 above theanti-cavitation plate 154 and selectively communicated with the branchpassages in accordance with operation of the flap valve member 164carried by the shaft 165 pivotally supported within the lower housingportion 153. The shaft 165 and valve member 164 are biased by a spring166 to close the branch passage 163 so that the housing passage 161normally communicates with the exhaust snout 156 through branch passage162. The branch passage 163 communicates with an opening 167 in the sideof the lower housing portion 153 beneath the anti-cavitation plate 154.A flexible and/or resilient valve member 168 is disposed on the exteriorof the housing portion 153 to cover the opening 167 and is secured tothe housing along its forward edge. The valve member 168 may be disposedin a depressed portion 169 provided in housing portion 153 so that thestreamlined contour of the housing is not unduly violated to accommodatethe valve member.

During forward drive operation of propulsion unit 152, the engineexhaust gases move through passage 161 and branch passage 162 fordischarge from the snout 156 into the outflow of the propellerslipstream.

When reverse drive operation of the propulsion unit 152 is contemplated,the reversing gear means 157 are engaged accordingly by correspondingrotation of the shift rod 159 and cam actuator 158. The shift rod 159simultaneously pivots the flap valve member 164 against the biasingpressure of spring 166 to open the branch line 163 and close the branchline 162. To effect this purpose the shift rod 159 carries an actuatorpin 170 which is engageable within a slot 171 of the link 172. FIG. 15generally shows the relationship of the actuator pin 170 in the slot 171in the neutral position of the shift rod 159 such that with clockwiserotation of the rod to the reverse drive position the link 172 is pulledand maintained forwardly by the actuator pin. Rearwardly the link 172 ispivotally connected at 173 to a lever 174 secured to the shaft 165.Thus, clockwise actuation of the lever 174 by the forward movement oflink 72 actuates the flap valve member 164 correspondingly to close thebranch passage 162. With the branch line 162 closed during reverse driveoperation of the propulsion unit 152, the engine exhaust gases flow frompassage 161 through branch passage 163 for discharge through the exhaustopening 167 past the valve member 168 into the outflow of the propellerslipstream.

When the reversing gear means 157 and shift rod 159 are returned to theneutral position the spring 166 is able to return the flap valve member164 to the position for closure of branch passage 163. With thepropulsion unit 152 underway in the forward direction, the valve member168 is maintained closed over the exhaust opening 167 by the waterflowing past the housing 153. 1 l

The test data presented in the table of FIG. 16 gives some indication ofthe substantial improvement in reverse propeller thrust to be derivedfrom utilization of this invention. The data was taken in connectionwith an outboard motor utilizing a through the propeller hub exhaustsystem with the engine operating at the engine speeds indicated incolumn A. A two bladed, 21 pitch propeller was employed in the test. Incolumns B, C and D the reverse thrust in pounds is recorded under thevarying test conditions indicated, namely, whether the exhaust dischargeopening at the rear of the propeller was open as indicated in columns Band C or closed as in column D and whether the propeller mountingprovided for a radial exhaust discharge opening forwardly of thepropeller resulting from separation between the propeller and adjacenthousing portion.

The data of FIG. 16 would seem to show that the solid flow of water tothe propeller and the reduction in exhaust back pressures during reverseoperation of the propulsion unit results in substantially improvedreverse propeller thrust giving rise to better economy and improvedcontrol and manueverability in the operation of the propulsion unit.

Further, a cavitating propeller or one that is working in an exhaust andwater environment can overspeed which may well lead to engine damage. Apropeller provided with a solid flow of water acts as a governor on theengine to preclude overspeeding. Thus, according to the presentinvention, such overspeeding is prevented regardless of the direction ofoperation of the propulsion unit.

I claim:

1. In an outboard propulsion unit driven by an internal combustionengine and having a reversible propeller to selectively drive the unitin the forward and rearward directions, said unit further having passagemeans for conducting exhaust gases from the engine through said unit anda first underwater exhaust discharge opening generally rearwardly of thepropeller and communicating with said passage'means to discharge theexhaust gases rearwardly of the propeller when the latter is operatingto drive the propulsion unit in the forward direction, said propulsionunit having a second underwater exhaust discharge opening forwardly ofthe propeller and communicating with said passage means and normallyclosed when the unit is driven in the forward direction, said secondexhaust discharge opening being adapted to open to discharge the exhaustgases forwardly of the propeller when the latter is operating to drivethe propulsion unit in the rearward direction.

2. in an outboard propulsion unit driven by an internal combustionengine and havinga reversible propeller to selectively drive the unit inthe forward and rearward directions, said unit further having passagemeans for conducting exhaust gases from the engine, means defining afirst underwater exhaust discharge opening generally rearwardly of thepropeller and communicating with said passage means to provide fordischarge of the exhaust gases rearwardly of the propeller when thelatter is operating to drive the propulsion unit in the forwarddirection, and means defining a second underwater exhaust dischargeopening forwardly of the propeller and communicating with said passagemeans and normally closed when the unit is driven in the forwarddirection, said second exhaust discharge opening being adapted to opento provide for discharge of exhaust gases forwardly of the propellerwhen the latter is operating to drive the propulsion unit in therearward direction.

3. The invention as set forth in claim 2 wherein the propeller isprovided with an exhaust passage communicating with the exhaust passagemeans of the propulsion unit and the means defining the first underwaterexhaust discharge opening is an opening from said exhaust passage at therear of the propeller.

4. The invention as set forth in claim 3 wherein valve means aredisposed in the exhaust discharge opening at the rear of the propellerto close the opening when the propulsion unit is operating in reverse.

5. The invention as set forth in claim 4 wherein the propeller iscarried on a generally horizontal and selectively reversible propellershaft rotatably supported by the propulsion unit and the valve meanscomprise an annular valve member carried by the propeller shaft,

said annular valve member being circumferentially en 7. The invention asset forth in claim 5 wherein the annular valve member carried by thepropeller shaft comprises a metal plate member.

8. The invention as set forth in claim 2 wherein the means defining thesecond underwater exhaust discharge opening is a radial opening formedby a separation between the propulsion unit and propeller.

9. The invention as set forth in claim 8 wherein the radial exhaustdischarge opening formed by a separation between the propulsion unit andpropeller is effected by reverse propeller thrust.

10. The invention as set forth in claim 8 wherein the radial exhaustdischarge opening formed by a separation between the propulsion unit andpropeller is effected by reverse propeller torque.

11. The invention as set forth in claim 8 wherein the propeller iscarried on a generally horizontal and selectively reversible propellershaft rotatably supported by the propulsion unit and the radial exhaustdischarge opening formed by a separation between the propulsion unit andpropeller is effected by axial movement of the propeller shaft.

12. The invention as set forth in claim 2 wherein the propulsion unitincludes an anti-cavitation plate and the means defining the firstunderwater exhaust discharge opening is an opening associated with saidanticavitation plate.

13. The invention as set forth in claim 2 wherein the propulsion unitincludes an anti-cavitation plate and the means defining the firstunderwater exhaust discharge opening is an exhaust snout projectingdownwardly from the anti-cavitation plate.

14. In an outboard propulsion unit driven by an inter.- nal combustionengine and having a housing portion including passage means forreceiving the exhaust gases from said engine, said housing portionhaving an opening rearwardly thereof communicating with said exhaustpassage means, said unit having a generally horizontal propeller shaftrotatably supported in said housing portion and projecting from theopening thereof and drivingly connected to the engine for selectiverotation in opposed directions in accordance with forward and reversedrive operation of the unit, a slip clutch'assembly mounted on therearwardly projecting portion of the propeller shaft for rotationtherewith, and a propeller carried on the slip clutch assembly andcomprising a pair of radially spaced hub sleeves connected by aplurality of vanes to form axially extending exhaust passages in thepropeller and terminating with an exhaust discharge opening rearwardlythereof, said propeller having a forward position wherein the outer hubsleeve is generally adjacent to and aligned with the opening in thehousing portion to place the propeller passages in communication withthe housing portion exhaust passage means whereby to conduct the engineexhaust gases rearwardly through the propeller for discharge from theexhaust discharge opening during forward drive operation of thepropulsion unit, said propeller being axially movable relative to thepropeller shaft and having a rearward position wherein the propeller isspaced from the housing portion to form a radial exhaust dischargeopening forwardly of the propeller for discharge of exhaust gases duringreverse drive operation of the propulsion unit.

15. The invention as set forth in claim 14 wherein the propeller isdrivingly connected to the slip clutch assembly by engagement ofcomplementary splines and stop means are provided on the propeller shaftat the respective ends of the slip clutch engageable by the propeller,and wherein said propeller is axially movable between the stop means inresponse to propeller thrust.

16. The invention as set forth in claim 14 wherein a valve retainingmember is disposed on the propeller shaft rearwardly of the slip clutchassembly and serves as stop means for movement of the propellerrearwardly, and an annular flexible valve member is disposed on theperiphery of said retaining member, said valve member being adapted toengage with the outer hub sleeve of the propeller to close the exhaustdischarge opening at the rear of the propeller when the propeller ismoved rearwardly-during reverse drive operation of the propulsion unit.

17. The invention as set forth in claim 16 wherein stop means engageableby the propeller are disposed on the propeller shaft forwardly of theslip clutch assembly, and a spring is disposed between the valveretaining member and the propeller to bias the propeller in thedirection of the stop means.

18. The invention as set forth in claim 16 wherein an annular offset isprovided in one of the adjacent faces of the inner hub sleeve and thevalve retaining member to form a spring seat, and a coil spring isdisposed on the propeller shaft between the inner hub sleeve and thevalve retaining member with one end thereof seated in the offset andserves to bias the propeller in the forward direction.

19. The invention as set forth in claim 14 wherein the propeller andslip clutch assembly are secured together to form a unitary assemblywhich is axially movable relative to the propeller shaft.

20. ln an outboard propulsion unit driven by an internal combustionengine and having a housing portion including passage means forreceiving the exhaust gases from said engine; said housing portionhaving an opening rearwardly thereof communicatingwith said ex haustpassage means; said unit having a generally horizontal propeller shaftrotatably supported in said housing portion and projecting from theopening thereof and drivingly connected to the engine for selectiverotation in opposed directions in accordance with forward and reversedrive operation of the unit; a propeller assembly comprising radiallyspaced first and second hub sleeves having an annular elastomericelement sandwiched therebetween to form slip clutch means, a third hubsleeve disposed radially outward from the second hub sleeve and carryingthe propeller blades, and a plurality of axially extending vanesconnecting the second and third hub sleeves to form exhaust passagestherebetween extending through the propeller assembly and terminatingwith an exhaust discharge opening rearwardly of the assembly; the innerfirst hub sleeve of said assembly being rotationally locked on thepropeller shaft to provide for rotation of the assembly with thepropeller shaft; said propeller assembly having a forward positionwherein the outer third hub sleeve overlaps within the opening in thehousing portion to peller assembly is spaced from the housing portion toform a radial exhaust discharge opening forwardly of the propellerassembly for discharge of exhaust gases during reverse drive operationof the propulsion unit.

21. The invention as set forth in claim 20 wherein axially spaced stopmeans are provided on the propeller shaft and the propeller assembly isaxially movable between the stop means in response to propeller thrust.

22. The invention as set forth in claim 20 wherein a valve retainingmember is disposed on the propeller shaft rearwardly of the propellerassembly and serves as a stop to interrupt movement of the propellerrearwardly and an annular flexible valve member is disposed on theperiphery of the retaining member, said valve member being adapted toengage with the outer third hub sleeve of the propeller assembly toclose the exhaust discharge opening at the rear of the assembly when thepropeller assembly is moved rearwardly during reverse drive operation ofthe propulsion unit.

23. The invention as set forth in claim 22 wherein stop means engageableby the propeller assembly are disposed on the propeller shaft forwardlyof the assembly, and a spring is disposed between the valve retainingmember and the propeller assembly to bias the as sembly in the directionof the stop means.

24. In a marine propulsion device comprising a lower unit including anexhaust gas discharge passageway terv minating in an exhaust gasdischarge port, a rotatably mounted porpeller shaft extending throughsaid port, a clutch mechanism selectively connecting said propellershaft in forward drive and in rearward drive and a propeller mounted onsaid propeller shaft for rotation therewith and including a blade havinga rear face and an exhaust gas passageway having an inlet communicatingwith said exhaust gas discharge port and an outlet rearwardly of saidblade, the improvement in combination therewith comprising means foraffording underwater exhaust gas discharge through said port and intothe water around said lower unit forwardly of the rear face of saidpropeller blade when said device is in reverse drive.

25; A device in accordance with claim 24 including means for preventingexhaust gas discharge through said outlet when said device is in saidreverse drive.

26. In a marine propulsion device comprising a lower unit including anexhaust gas discharge passageway terminating in an exhaust gas dischargeport, a rotatably mounted propeller shaft extending through said port,and a propeller mounted on said propeller shaft for rotation therewithand including an exhaust gas duct having an inlet located in a positiondirectly communicating with said exhaust gas discharge port, theimprovement in combination therewith comprising means for affordingaxially shifting of said propeller relative to said discharge portbetween said position wherein said discharge port and said inlet are indirect communication and a second position wherein said discharge portand said inlet are in spaced relation to each other to provide anopening for exhaust gas discharge forwardly of said propeller.

27. A marine propulsion device according to claim 26 wherein said meansfor affording axial shifting of said propeller relative to saiddischarge port comprises cooperating means on said propeller shaft andon said propeller affording axial shifting of said propeller on saidpropeller shaft.

1. In an outboard propulsion unit driven by an internal combustionengine and having a reversible propeller to selectively drive the unitin the forward and rearward directions, said unit further having passagemeans for conducting exhaust gases from the engine through said unit anda first underwater exhaust discharge opening generally rearwardly of thepropeller and communicating with said passage means to discharge theexhaust gases rearwardly of the propeller when the latter is operatingto drive the propulsion unit in the forward direction, said propulsionunit having a second underwater exhaust discharge opening forwardly ofthe propeller and communicating with said passage means and normallyclosed when the unit is driven in the forward direction, said secondexhaust discharge opening being adapted to open to discharge the exhaustgases forwardly of the propeller when the latter is operating to drivethe propulsion unit in the rearward direction.
 2. In an outboardpropulsion unit driven by an internal combustion engine and having areversible propeller to selectively drive the unit in the forward andrearward directions, said unit further having passage means forconducting exhaust gases from the engine, means defining a firstunderwater exhaust discharge opening generally rearwardly of thepropeller and communicating with said passage means to provide fordischarge of the exhaust gases rearwardly of the propeller when thelatter is operating to drive the propulsion unit in the forwarddirection, and means defining a second underwater exhaust dischargeopening forwardly of the propeller and communicating with said passagemeans and normally closed when the unit is driven in the forwarddirection, said second exhaust discharge opening being adapted to opento provide for discharge of exhaust gases forwardly of the propellerwhen the latter is operating to drive the propulsion unit in therearward direction.
 3. The invention as set forth in claim 2 wherein thepropeller is provided with an exhaust passage communicating with theexhaust passage means of the propulsion unit and the means defining thefirst underwater exhaust discharge opening is an opening from saidexhaust passage at the rear of the propeller.
 4. The invention as setforth in claim 3 wherein valve means are disposed in the exhaustdischarge opening at the rear of the propeller to close the opening whenthe propulsion unit is operating in reverse.
 5. The invention as setforth in claim 4 wherein the propeller is carried on a generallyhorizontal and selectively reversible propeller shaft rotatablysupported by the propulsion unit and the valve means comprise an annularvalve member carried by the propeller shaft, said annular valve memberbeing circumferentially engageable within the propeller exhaustdischarge opening to substantially seal the opening.
 6. The invention asset forth in claim 5 wherein the annular valve member carried by thepropeller shaft comprises a resilient member.
 7. The invention as setforth in claim 5 wherein the annular valve member carried by thepropeller shaft comprises a metal plate member.
 8. The invention as setforth in claim 2 wherein the means defining the second underwaterexhaust discharge opening is a radial opening formed by a separationbetween the propulsion unit and propeller.
 9. The invention as set forthin claim 8 wherein the radial exhaust discharge opening formed by aseparation between the propulsion unit and propeller is effected byreverse propeller thrust.
 10. The invention as set forth in claim 8wherein the radial exhaust discharge opening formed by a separationbetween the propulsion unit and propeller is effected by reversepropeller torque.
 11. The invention as set forth in claim 8 wherein thepropeller is carried on a generally horizontal and selectivelyreversible prOpeller shaft rotatably supported by the propulsion unitand the radial exhaust discharge opening formed by a separation betweenthe propulsion unit and propeller is effected by axial movement of thepropeller shaft.
 12. The invention as set forth in claim 2 wherein thepropulsion unit includes an anti-cavitation plate and the means definingthe first underwater exhaust discharge opening is an opening associatedwith said anti-cavitation plate.
 13. The invention as set forth in claim2 wherein the propulsion unit includes an anti-cavitation plate and themeans defining the first underwater exhaust discharge opening is anexhaust snout projecting downwardly from the anti-cavitation plate. 14.In an outboard propulsion unit driven by an internal combustion engineand having a housing portion including passage means for receiving theexhaust gases from said engine, said housing portion having an openingrearwardly thereof communicating with said exhaust passage means, saidunit having a generally horizontal propeller shaft rotatably supportedin said housing portion and projecting from the opening thereof anddrivingly connected to the engine for selective rotation in opposeddirections in accordance with forward and reverse drive operation of theunit, a slip clutch assembly mounted on the rearwardly projectingportion of the propeller shaft for rotation therewith, and a propellercarried on the slip clutch assembly and comprising a pair of radiallyspaced hub sleeves connected by a plurality of vanes to form axiallyextending exhaust passages in the propeller and terminating with anexhaust discharge opening rearwardly thereof, said propeller having aforward position wherein the outer hub sleeve is generally adjacent toand aligned with the opening in the housing portion to place thepropeller passages in communication with the housing portion exhaustpassage means whereby to conduct the engine exhaust gases rearwardlythrough the propeller for discharge from the exhaust discharge openingduring forward drive operation of the propulsion unit, said propellerbeing axially movable relative to the propeller shaft and having arearward position wherein the propeller is spaced from the housingportion to form a radial exhaust discharge opening forwardly of thepropeller for discharge of exhaust gases during reverse drive operationof the propulsion unit.
 15. The invention as set forth in claim 14wherein the propeller is drivingly connected to the slip clutch assemblyby engagement of complementary splines and stop means are provided onthe propeller shaft at the respective ends of the slip clutch engageableby the propeller, and wherein said propeller is axially movable betweenthe stop means in response to propeller thrust.
 16. The invention as setforth in claim 14 wherein a valve retaining member is disposed on thepropeller shaft rearwardly of the slip clutch assembly and serves asstop means for movement of the propeller rearwardly, and an annularflexible valve member is disposed on the periphery of said retainingmember, said valve member being adapted to engage with the outer hubsleeve of the propeller to close the exhaust discharge opening at therear of the propeller when the propeller is moved rearwardly duringreverse drive operation of the propulsion unit.
 17. The invention as setforth in claim 16 wherein stop means engageable by the propeller aredisposed on the propeller shaft forwardly of the slip clutch assembly,and a spring is disposed between the valve retaining member and thepropeller to bias the propeller in the direction of the stop means. 18.The invention as set forth in claim 16 wherein an annular offset isprovided in one of the adjacent faces of the inner hub sleeve and thevalve retaining member to form a spring seat, and a coil spring isdisposed on the propeller shaft between the inner hub sleeve and thevalve retaining member with one end thereof seated in the offset andserves to bias the propeller in the forward direction.
 19. The inventionas set forth in claim 14 wherein the propeller and slip clutch assemblyare secured together to form a unitary assembly which is axially movablerelative to the propeller shaft.
 20. In an outboard propulsion unitdriven by an internal combustion engine and having a housing portionincluding passage means for receiving the exhaust gases from saidengine; said housing portion having an opening rearwardly thereofcommunicating with said exhaust passage means; said unit having agenerally horizontal propeller shaft rotatably supported in said housingportion and projecting from the opening thereof and drivingly connectedto the engine for selective rotation in opposed directions in accordancewith forward and reverse drive operation of the unit; a propellerassembly comprising radially spaced first and second hub sleeves havingan annular elastomeric element sandwiched therebetween to form slipclutch means, a third hub sleeve disposed radially outward from thesecond hub sleeve and carrying the propeller blades, and a plurality ofaxially extending vanes connecting the second and third hub sleeves toform exhaust passages therebetween extending through the propellerassembly and terminating with an exhaust discharge opening rearwardly ofthe assembly; the inner first hub sleeve of said assembly beingrotationally locked on the propeller shaft to provide for rotation ofthe assembly with the propeller shaft; said propeller assembly having aforward position wherein the outer third hub sleeve overlaps within theopening in the housing portion to place the propeller assembly passagesin communication with the housing portion exhaust passage means wherebyto conduct the engine exhaust gases rearwardly through the propellerassembly for discharge from the exhaust discharge opening during forwarddrive operation of the propulsion unit; said propeller assembly beingaxially movable relative to the propeller shaft and having a rearwardposition wherein the propeller assembly is spaced from the housingportion to form a radial exhaust discharge opening forwardly of thepropeller assembly for discharge of exhaust gases during reverse driveoperation of the propulsion unit.
 21. The invention as set forth inclaim 20 wherein axially spaced stop means are provided on the propellershaft and the propeller assembly is axially movable between the stopmeans in response to propeller thrust.
 22. The invention as set forth inclaim 20 wherein a valve retaining member is disposed on the propellershaft rearwardly of the propeller assembly and serves as a stop tointerrupt movement of the propeller rearwardly and an annular flexiblevalve member is disposed on the periphery of the retaining member, saidvalve member being adapted to engage with the outer third hub sleeve ofthe propeller assembly to close the exhaust discharge opening at therear of the assembly when the propeller assembly is moved rearwardlyduring reverse drive operation of the propulsion unit.
 23. The inventionas set forth in claim 22 wherein stop means engageable by the propellerassembly are disposed on the propeller shaft forwardly of the assembly,and a spring is disposed between the valve retaining member and thepropeller assembly to bias the assembly in the direction of the stopmeans.
 24. In a marine propulsion device comprising a lower unitincluding an exhaust gas discharge passageway terminating in an exhaustgas discharge port, a rotatably mounted porpeller shaft extendingthrough said port, a clutch mechanism selectively connecting saidpropeller shaft in forward drive and in rearward drive and a propellermounted on said propeller shaft for rotation therewith and including ablade having a rear face and an exhaust gas passageway having an inletcommunicating with said exhaust gas discharge port and an outletrearwardly of said blade, the improvement in combination therewithcomprising means for affording underwater exhaust gas discharge throughsaid port and into the waTer around said lower unit forwardly of therear face of said propeller blade when said device is in reverse drive.25. A device in accordance with claim 24 including means for preventingexhaust gas discharge through said outlet when said device is in saidreverse drive.
 26. In a marine propulsion device comprising a lower unitincluding an exhaust gas discharge passageway terminating in an exhaustgas discharge port, a rotatably mounted propeller shaft extendingthrough said port, and a propeller mounted on said propeller shaft forrotation therewith and including an exhaust gas duct having an inletlocated in a position directly communicating with said exhaust gasdischarge port, the improvement in combination therewith comprisingmeans for affording axially shifting of said propeller relative to saiddischarge port between said position wherein said discharge port andsaid inlet are in direct communication and a second position whereinsaid discharge port and said inlet are in spaced relation to each otherto provide an opening for exhaust gas discharge forwardly of saidpropeller.
 27. A marine propulsion device according to claim 26 whereinsaid means for affording axial shifting of said propeller relative tosaid discharge port comprises cooperating means on said propeller shaftand on said propeller affording axial shifting of said propeller on saidpropeller shaft.